Numerous types of float switches are known. They may be physically integrated with the devices they control, or physically independent and connected to those devices mechanically or electrically. Again, the float itself may be mechanically connected to the electrical contacting elements, for switching at a site more or less remote from the actual float, or the contacting element may be made a part of a float from which electrical rather than physical connections are extended.
Previous float switches have been characterized by a rather limited range of operation, relatively complicated physical or electrical insulation details, and difficulty of access for repair or maintenance, particularly when the unit to be controlled is in a submerged location.
The limited range of operation is because switches suitable for this use have a quite small "differential", which is to say that there is only a relatively small angular difference between the position in which the switch operates in the "ON" sense and the position in which it operates in the "OFF" sense. A narrow differential is an advantage when it is desired, for example, to hold the level of a liquid in a container as nearly constant as possible, but there are other occasions in which it is permissible to manage a liquid control system so that the liquid is pumped to a first level, the pump is deenergized, and the liquid is allowed to fall or rise to a very different level before pump operation is resumed: examples are filling reservoirs and emptying sumps. In these applications switches having narrow differentials cause repeated brief pump operation at intervals of undesirably short duration.